Viscose process and apparatus



`Iuly 13,1937.` w. H. BRADSHAW ET AL 2,087,016 vIscosE rRocEss ANDAPPARATUS Filed July i3, 1934 EDWARD I2. MKEE A ATTOR EY.

Patented `luly 13,- 1937 UNITED STATES PATEn'r oFFicE 2,087,016 lviscosa PROCESS AND .dermatitis William Henry Bradshaw, Bualo, N. Y.,and

Edward R. McKee, ,Eer-mittags, Te., signors, by mesne assients, to llont-de Nemours s llompany,

mi; it. t., en wiimingten,

Del., a corporation of Delaware E Application .miv it, naar, senat ne.,essere 9 Claims..

This invention relates to a Viscose process. More particularly, theinvention has to do with the treatment of substantially ripened viscoseand the feeding thereof to the product-forming room.

The invention `will be described for convenience in its application to aprocess of making rayon, but the process is equally applicable to themanufacture of regenerated cellulose sheeting, or to any other processin which viscose is used.

In the manufacture of rayon by the viscose' process, cellulose xanthateis formed in a manner which will be understood by those skilledl in theart, is dissolved, lis ripened, is filtered, is

deaerated, and is extruded through a spinneret into a coagulating bath.The relation between the viscose solution andthe coagulatingl bath isadjusted to produce yarn of the desired properties. The maintenance ofthis relation is. essential in the production of a uniform product. ItA

is relatively easy to maintain thev coagulating bath at a constantvalue, but is diihcult to maintain the viscose a't a constant valuebecause it changes with time and at different rates depending on thetemperature. 'I'his change in the viscose is called ripening and theriper the viscose the more easily it coagulates. Viscose coagula-.

bility or its degree of ripeness is commonly measured in terms of saltindex. The salt index referred to in this specification is that definedby Reinthaler and Rowe in Artificial silk, page 68, second fullparagraph, published in 1929.*

In the prior art the salt index of the viscose delivered to the spinningroom has been controlled to within plus or minus 0.5, but this givesrise to a non-uniform product.

In the practice of today, batches of cellulose xanthateare dissolved inan aqueous caustic solution and vthree or four such charges blended v toform a'nal viscose charge. These charges aresent to the ripeningroom,\are confined in tanks, filtered, confined in other tanks, andthe'pro'cesses of filtering and confining repeated until the viscose hasreached thel stage *The degree of ripeness of the viscose is determinedby introducing small samples into common salt solutions of differentconcentrations. The fresher and less ripe the viscose, the stronger thesolution 'of common salt of a common salt correct degree of necessary toprecipitate the sodium cellulose xanthate. The salting point" of aviscose signifies the concentration solution that just suffices tocoagu- ,late a drop of viscose which is allowed to fall into it. Thedegree of ripencss most favourable for spinning is dependent uponvarious factors, e. g., the nature of the preparation of the viscose,the composition and tempcrature of lthecoagulatinf.: bath, etc, In thecase of a viscose prepared as already described, for example, theripeness has -been attained when it is coagulatd by 3-4% common saltsolution. Such viscose, therefore, has a salting point of 3-4.

- is further non-uniformity of the product arising process of preparingviscose.

of viscose must be left in each of these tanks to 10 prevent air fromblowing through and getting in the viscose pipe lines, otherwisecontinuous filaments or sheets could not be formed in an orderly mannerand without excessive diiiculty. When a feed tank is refilled with freshviscose, the heel from the charge previously inthat tank has quite adiiferent salt index than the salt index of the new charge and since thetwo charges do not intermingle appreciably but remain substantially indistinct layers, it is impossible to deliver to the product-forming roomuniform viscose or one having anywhere near a constant salt index. Inaddition, since the viscose musttravel diiferent distances through pipesin the relatively warm product-forming room to various machines, therefrom the varying amount of ripening of the viscose that takes place inthis travel.

It is an object of this invention to improve the Another object of theinvention is to prepare viscose having a. substantially uniform saltindex. Still another Aobp ject is to deliver to the product-forming rooma viscose having substantially constant salt' index and to maintain thatsalt index substantially con- 3f stant at all the extrusion devices orproduct-forming machines in that room. Other objects of theinventionwill be in part apparent and in part 4 set forth hereinafter, yp

These objects are accomplished by the improved 0 means and methodhereinset forth and claimed. The drawing is a diagrammatic ow sheet representing one mode of practicing the invention.

Referring to the drawing; numerals IA, IB and IC refer to dissolvingtanks which perform the function of dissolving the cellulose xanthate inan aqueous caustic solution. These :dissolvers may be three in number,as shown, or more' or less. The batches ofv viscose from the severaldissolvers pass through valve-controlled pipelines l0 leading from thevdissolvers to a blender 2 in whichthe batches of viscose are mixedtogetherin order to improve the homogeneity of the product. The blenderis of any satisfactory type known to the art. The blended viscose passes56 from the blender ythrough valve-controlled line 20 to the first of anumber of ripening tanks,3A, 3B, 3C, etc., to which the charge from theblender is transferred. These ripening tanks are located in a room keptat constant temperature. The charges of viscose are advanced from oneripening tank to another through pipelines, which may bevalve-controlled as shown, as the older viscose is consumed and duringthis advance, they are filtered through successively finer filteringmedia. For instance, the relatively green viscose is passed through afilter press 3|, connected between tanks 3D and 3E by means of pipelineswhich may be valve-controlled. Between tanks 3K and 3L there may beanother filter similarly located, having somewhat finer filter cloths,and further on, between tanks 3P and 3R, a third filter press may besimilarly located, having a still finer filtering medium. After the lastfiltration, the viscose is stored under high vacuum, in order that theentrapped air be removed, in partly filled tanks 3R, 3S and 3T,connected to each other and to the filter press 33 by means ofvalvecontrolled pipelines as shown. The filtered, airfree viscose isthen flowed from tank 3T by means of valve-controlled lines 330, 33| and332 alternately to feed tanks 4A and 4B.

Viscose is pumped or otherwise flowed alternately from the tanks 4A and4B, through valvecontrolled pipelines 43|, 432 and 433 to a pump 5 whichmay be of any suitable type but preferably is a constant delivery pumpdriven by an electric motor. 'I'he pump discharges the viscose into ahomogenizer 6, which may be any suitable blending means. The homogenizeris so constructed that the two viscoses (the second of which will bedescribed hereinafter) fed thereinto will be thoroughly blended togetherto form a homogeneous mixture. The viscose passes on from thehomogenizer tank 6 through valve-controlled pipe and into the agitatedline tank 1. This agitated line tank contains agitating means whichpreferably is a relatively slowly revolving paddle which will notviolently disturb the surface of the viscose and permit air to beentrapped therein. It should be understood, however, that thoroughmixing of the viscose leaving the homogenizer with that in the agitatedline tank must be provided to prevent pocketing or by-passing ofunblended viscose. The volume of the agitated line tank should besufiiciently large to suppress fluctuations in index but not so large asto cause an excessive salt index drop from the feed tank to it. Ingeneral, the capacity of this tank should be about that of one of thefeed tanks. This agitated line tank is jacketed preferably to abouttwo-thirds the height of the tank or to about the normal viscose level.This jacketed space is connected with warm and cold l waterlines or withother temperature control media such as brine. The homogenizer may alsobe jacketed for temperature control.

The viscose flowing into tank 1 should preferably enter below theviscose level therein. A porc tion of the viscose is drawn from thebottom of this tank through valve-controlled line II-'I2 by means ofpump 8, which is set to deliver viscose throughA line 8| in excess ofthe require-v ments of the spinning machines or to other machines forforming shaped articles. A pressure control Valve 83 maintains thepressure in the feed line 82 constant by permitting a certain quantityvof viscose to return by means of lines 84 and 14 through pump 5 andhomogenizer 6 to blend with the viscose coming from one of the icedtanks 4A or 4B. If it is found desirable, a filter press may be locatedbetween pump 8 and the extrusion devices in order to insure thecleanliness of the viscose.

In the practice of our invention, viscose is fed continuously into thehomogenizer and blending system from one of the two feed tanksalternately. This viscose is passed through pump 5 to homogenizer 6along with approximately 10 times its volume of viscose taken from linetank Afterpassing through homogenizer 6, it is i'ed into the line tankimmediately below the surface of the viscose therein. In passing downthrough line tank 1, it is blended with the Viscose in the tank andemerges from the bottom of the tank, being then fed in part to the feedline 82. By this system of operation, even though the small heel of theprevious charge in the feed tank may have an index so far below thebalance of the charge that it would not produce a good product, itbecomes so thoroughly and completely blended with the large volume ofthevmaterial in line tank 1 that the index of the viscose leaving linetank and going to feed line 82 is changed but very slightly. y

In addition to correcting the Variations that arise from the periodicpassage of these small heels and other small amounts of viscose havingsimilar, greatly different indices, the volume of viscose in thissystemand the close control of it permit to a very great degree theneutralizing of other types of index variation of comparatively shortduration and is therefore a useful means of insuring a constant supply,to the extrusion room, of uniform viscose. 4

For example, if the index of the charge of viscose being drawn from thefeed tank is abnormally high, viscose of the standard salt index can bedelivered to the spinning room by temporarily reducing the volume ofViscose fed into this system from the feed tanks and if necessary byincreasing the temperature of the' viscose in the homogenizer and in theline tanks. l

Thus the operation of the plant is considerably facilitated and it ispossible to produce a product far superior to that produced heretofore.

By the process just previously described, we are able to deliver viscosehaving a substantially constant salt index to the spinning room.However, since the viscose must be conducted various distances or forvarious lengths of time through pipes in the relatively warm spinningroom, in order to reach all the machines and spinning positions therein,it becomes further and non-uniformly ripened. This variation in ripeningas measured by salt index of Viscose taken from various machines andvarious spinning positions may be as much as 0.3 or even more.

In order to diminish this variation and improve the uniformity of theproducts formed, we incorporate in the viscose an agent that inhibits orretards further ripening of the Viscose. For instance, we may add asmall amount of sodium sulfite, such as 0.1% to 5% or more andpreferably about 1%, based on the cellulose content of the viscose. Theaddition may be made either as a solution or as a solid. When we add tothe viscose 1% of sodium sulte based on the cellulose content of theviscose, we find the uniformity of the viscose as measured by salt indexis improved throughout the spinning room about three-fold. The additionof the inhibitor is preferably made to the thoroughly blended viscosedescribed above as it leaves the system in line 82. It is to beunderstood that suitable precaution will be taken to

